1. Field of the Invention
The invention relates generally to the design of anchoring slip assemblies and, in particular aspects, to the design of liner hanger devices used for suspending a liner within a wellbore.
2. Description of the Related Art
A liner is a tubular member that is usually run inside of wellbore casing and suspended within it. Liners are typically secured within a wellbore by toothed slips that are located on liner hangers. The slips are set by axially translating them with regard to the liner hanger mandrel. As the slips are translated axially, they are cammed radially outwardly by a ramped surface that is fashioned into the mandrel. As the slips move radially outwardly, toothed outer surfaces of the slip will bitingly engage the surrounding casing. This type of arrangement is shown, for example, in U.S. Pat. No. 4,497,368 issued to Baugh, wherein slips that are radially expanded by riding up over cone elements fashioned into the tubular body of the central mandrel. U.S. Pat. No. 5,086,845 issued to Baugh and U.S. Pat. No. 6,431,277 issued to Cox et al. each describe a hanger arrangement wherein load is transferred circumferentially through the slip seat. U.S. Pat. Nos. 4,497,368, 5,086,845, and 6,431,277 are all owned by the assignee of the present invention and are incorporated herein by reference.
A problem with this standard slip setting arrangement is that the amount of radial expansion of the slip elements is limited. The depth of the slip ramp, and thus the amount of camming, is largely limited by the thickness of the slips and slip seat in the mandrel body. These thicknesses are close to the same, with the slips usually being slightly thinner than the slip seat so that the teeth of the slips will not be exposed over the slip seat when the slip is not set. If the needed camming distance is defined as the distance between the outer diameter of the tool and the inner diameter of the casing to hang in, then it is entirely limited by the thickness of the slip. The slip, in turn, is limited in thickness by the stipulation that it rests on the mandrel body and should be thinner than the slip seat. This restriction can be broken by reducing the outer diameter of the portion of the mandrel over which the slips sit. However, this reduced outer diameter and mandrel thickness would result in a decreased pressure rating for the tool, which is undesirable.
A further limitation to camming distance relates to the mechanism used to retain the non-cammed end of the slip element in place upon the mandrel body. In U.S. Pat. No. 5,086,845, the slips are not restrained by any type of structure. However, an overlying tab was later introduced to hold the lower ends of slips in place. This tab arrangement also limits the setting distance of the slips by reducing the degree of freedom of movement that the slip elements have.
The present invention addresses the problems of the prior art.